Electric heating system control



Aug. 10, 1937. 1 CUNNINGHAM 2,089,826

ELECTRIC HEATING SYSTEM CONTROL Original Filed May 27, 1933 29 :26 f 47 I 1p glvmic/wto'n Lewis L. Cunningham WWW Patented Aug. 10, 1937 "PATENT OFFICE ELECTRIC HEATING SYSTEM CONTROL Lewis L. Cunningham,

Minneapolis, Minn., as-

signor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation Delaware Original application May 27, 1933, Serial No. 673,236. Divided and this application July 9, 1935, Serial No. 32,223

7 Claims.

The present invention relates to the control of temperature changing systems and particularly those in which heat is generated electrically as by passing current through suitable resistors.

The object of the invention is the provision of a temperature changing system in which the flow of current to an electrical temperature changing means, such as a heating resistor or resistors, is controlled by an induction voltage regulator that is in turn controlled by a novel electrically balanced proportioning or graduated control apparatus.

For a more complete understanding of the invention, reference may be had to the following detailed description and accompanying single drawing which is a diagrammatic showing of one form of the invention.

This application is a division of my copending application Serial No. 673,236, filed May 27, 1933 and entitled Remote control systems.

" Referring to the single drawing, there is shown a control potentiometer comprising a control resistance III which is contacted by a movable member herein shown as actuated by a bimetallic element l2 which may respond, for instance, to the temperature of an industrial iurnace. In actual commercial construction, the movable member II is operated by any of the well-known mechanisms controlled by a thermo- 0 couple such as a Leeds and Northrup controller.

The system 01' the present invention further includes a pair of solenoid coils l3 and I4 which control a plunger l5 that is connected to a flexible switch arm l6 by means of a light spring |1. One end 01' control resistance I6 is connected to solenoid coil l3 through a protective resistance l8 by means of wires l9 and 20. The other end of control resistance It is connected to one end of solenoid coil |4 through a protective resistance 0 2| by means 01' wires 22 and 23. Line wires 24 and 25 supply power to the primary 26 of a stepdown transformer having a low voltage secondary 21. Wire 26, and therefore one end of solenoid coil 3, is connected to one side of secondary 21 by means of wires 28 and 29. In like manner, wire 23, and therefore one end of solenoid coil I4, is connected to the other side of secondary 21 by means of wires 36 and 3|.

The flexible switch arm l6 carries movable contacts 32 and 33 which are adapted to respectively engagestationary contacts 34 and 35. The system further includes a balanced relay having windings 36 and 31, the junction of which is connected to flexible switch arm l6 through a protective resistance 38 by means of wires 39 and 40. The other end of relay winding 36 is connected to stationary contact 35 by wires 5| and 52 and is connected to one side of secondary 21 by wires 5|, 53, and 3|. The outer end of relay winding 31 is connected to stationary contact 34 by wires 54 and 55 and is connected to the other side of secondary 21 by wires 54, 56 and 29.

Relay windings 36 and 31 control a plunger 51 which is connected to a relay switch arm 58 through a light spring 59. Relay switch arm 58 carries movable contacts 66 and 6| which are respectively cooperable with stationary contacts 62 and 63.

The switch arm 58 and associated contacts control first and, second relays. The first relay comprises a relay coil 64 which controls an armature 65 to which are secured switch arms 66 and 61 that are adapted to respectively engage contacts 68 and 69 upon energization of relay coil 64. The second relay comprises a relay coil 16 which controls an armature 1| to which are secured switch arms 12 and 13 that are adapted to respectively engage contacts 14 and 15 upon energization of relay coil 10.

The first and second relays control an induction voltage regulator which comprises a threephase motor 16 which operates a movable element or armature 11. The induction voltage regulator includes windings 18 and 19; the latter of which is positioned by movable element or armature 11 as is well-known by those skilled in the art.

A balancing potentiometer is comprised by a balancing resistance and a balancing contact finger 8| which-is actuated by a link 82 that is connected to movable element or armature 11 for reciprocation thereby. One end of balancing resistance 80 is connected to one end of control resistance l0 and to wire I9 by a wire 83. The

other end of balancing resistance 86 is con-- nected to the other end of control resistance l6 and to wire 22 by a wire 84. Wires 85,86, and 81 interconnect balancing contact finger 8|, movable member II, and the junction of solenoid coils l3 and I4.

The induction voltage regulator controls the voltage impressed upon an electric heating means, herein shown as a single electrical resistance 88, which may heat an electric furnace, the temperature of which is to be controlled by the present system due to the response of bimetal-. lic element I2.

A three-phase source of power is indicated by line wires 89, and 9|. Line 89 is connected to the junction of coils l8 and 73 by a wire 92. The other end of winding 78 is connected to heating resistance 88 by a wire 93. The other end of heating resistance 88 is connected to the lower end of winding 19 and to line 90 by wires 96, 95, and 96. The remaining circuit connections will be described under the heading Operation.

A single phase voltage induction regulator and a single heater 88 have been shown for simplicity. In actual practice a three-phase voltage induction regulator and a three-phase heater would be used as will be appreciated by those skilled in the art.

Operation With the parts in the position shown wherein movable member II is contacting the centerof control resistance It and balancing contact finger al is contacting the center of balancing resistance 80, the voltage drops across solenoid coils I3 and I4 are equal. Contacts 32 and 33 are therefore out of engagement with contacts 3 3 and 35 with the result that relay windings 36 and 31 are equally energized 'since they are connected in series across secondary 21. Contacts 60 and 6! are therefore out of engagement with contacts 62 and 63. Relay coils 6d and B0 are both deenergized and heating resistance B8is supplying Just-enough heat to maintain the furnace temperature at the desired point.

Now if the furnace temperature should rise, bimetallic element I2 in responding to such a rise in furnace temperature moves movable member II along control resistance I0 toward the left hand end thereof, thereby increasing the voltage drop across solenoid coil i i and decreasing the voltage drop across solenoid coil I3, whereby plunger I5 moves to the right and causes contact 32 to engage contact 34. En-

gagement of contact 32 with contact 36 places.

cuit which is as follows: line 26, wire 9?, switch arm 58, contacts 6| and 63, wire 98, relay coil 64, wire 99 and wire l00.to line 25. Armature 65 is attracted and moves switch arms 66 and 61' into engagement with contacts 88 and 69. Two cir cuits are thus established to three-phase motor 76. The first circuit is as follows: line 89, wire IOI, motor 16, wire I02, wire I03, contact 68, switch arm 66, wire I04, and wire I05 to line 90. The second circuit is as follows: line 89, wire IOI,' motor 16, wire I06, wire ill'l, contact 69, switch arm 61, wire I08, and wire I09 to line 9|. Motor 16 will now begin to rotate movable element or armature T! in a counter-clockwise direction through suitable reduction gearing generally indicated at H0. Such movement of movable element 1'! slowly moves winding 19 in respect to winding 18, as is well-known to those skilled in the art, with the result that the voltage impressed across heating resistance 88 is reduced so as to reduce the amount of heat furnished by heating resistance 88. Link 82 will be moved to the right and carries with it balancing contact finger 8! which rebalances the voltage drops across solenoid coils I3 and M when balancing contact finger M has been moved to the proper position along balancing resistance 80.

Rebalancing of the voltage drops across solenoid coils I3 and It causes plunger I5 to move to the left until it reaches its normal central position. This movement of plunger i5 disengages contact 32 from contact 34 whereby the circuit through protective resistance 38 is interrupted. Interruption of the circuit through resistance 38 rebalances the voltage drops across and the current flows through relay windings 36 and 31 whereupon plunger 5i is moved to the right until its normal central position is reached. Contact 68 is thereby moved out of engagement with contact 63 to deenergize relay coil 64, whereupon armature 65 moves by gravity to the position shown thereby interrupting the two circuits to three-phase motor it.

The parts will remain in their new positions until there is a further change in furnace temperature. If the furnace temperature should again rise, movable member I! will .be moved nearer to the left-hand end of control resistance It and the above described sequence of operations will be repeated. When the furnace temperature falls, bimetallic element I2 moves movable member Ii along control resistance I0 towards the right-hand end thereof. This action increases the voltage drop across solenoid coil I3 and decreases the voltage drop across solenoid coil .M which results in movement of plunger I5 to the left. Contact 33 is thereby moved into engagement with contact 35 whereupon protec-' tive resistance 38 is placed in parallel with relay winding 36 and the current flow through protective resistance 38 and relay winding 36 all traverses relay winding 31. Plunger 5'! is therefore moved to the right causing contact 60 to engage contact 62.

Engagement of contact 60 with contact 62 energizes relay coil 10 by a circuit which-is as follows: line 26, wire 91, relay switch arm 58, contacts 60 and 62, wire III, relay coil 10, wire H2, and wire 800 to line 25. Energization of relay coil 10 attracts armature 'II which in turn moves switch arms 12 and I3, respectively, into engagement withcontacts l4 and 15. Two energizing circuits are therefore established for threephase motor it which circuits rotate said motor E6 in adirection opposite. to. that to which it was formerly rotated. The first of these circuits is as follows: line 89, wire IUI, motor 16, wire I03, wire H3, contact I5, switch arm 13, wire H4, and wire I09 to line 9|. The second new energizing circuit for motor 16 is as follows: line 89, wire IOI, motor '76, wire I06, wire H5, contact 74, switch arm i2, wire H6, and wire I05 to line 90.

Movable element or armature 71 is therefore rotated in a clockwise direction and moves balancing contact finger 8i along balancing resistance 86 toward the leftend thereof by means of link 82 and also moves winding 19 in respect to winding 78 in a direction to increase the voltage impressed across heating resistance 88. This action will continue until the amount of heat delivered by heating resistance 88 is sufiicient to prevent further drop in furnace temperature and the furnace temperature levels off at some constant value. At this time balancing contact finger BI will be in contact with that portion of balancing resistance which rebalances the voltage drops across solenoid coils I3 and I4.

Plunger I5 is thereupon moved to its normal central position to interrupt the circuit through protective resistance 38 by separating contacts 33 and 35. The current flows through relay aooaaao windings 36 and 31 are thereby equalized and plunger 51 returns to its normal central poation to interrupt the circuit through relay coil II by separating contacts 60 and 62. Armature ll moves under the influence of gravity to the position shown and interrupts the two above described energizing circuits for three-phase motor It.

In this manner, the heating effect of heating resistance 88 is decreased or increased as the furnace temperature rises above or falls below normal and this decrease or increase in the heating eifect of heating resistance 88 is proportional to the departure of the furnace temperature from the desired normal. This is accomplished by automatically operating the movable element of a three-phase induction voltage regulator. The temperature range within which the temperature is thus allowed to fluctuate may be predetermined, within reasonable limits, by so adjusting or constructing the furnace temperature responsive mechanism that the movable member ll moves from one end of control resistance 10 to the other end thereof when the furnace temperature changes from one of its predetermined limits to the other of its predetermined limits.

From the foregoing description of the invention, it will be apparent that I have provided a novel temperature control system in which many changes and rearrangements may be made without departing from the spirit thereof, wherefore I am to be limited only by the scope of the appended claims.

I claim:

1. In an electrically controlled heating system, in combination, electrical heating means which varies its heating effect in accordance with the voltage impressed thereon, an induction voltage regulator in control of the voltage impressed upon said heating means, said induction voltage regulator including a movable element which causes variation in the voltage impressed upon the heating means when said element is moved, three-phase reversible motor means in control of said movable element to position the same,

first and second relays, two circuits for said motor means controlled by each of said relays, one set of said circuits operating said motor means in one direction and the other set operating the motor means in the other direction, double circuit switching means in control of said relays to selectively energize the same, or deenergize both of them, a condition responsive controller,,and means including connections between said controller, switching means and movable element by which movement of said controller to a new position operates said switching means to energize one or the other of said relays to cause movement of said movable element in a direction to deenergize such relay.

2. In an electrically controlled heating system, in combination, electrical heating means which varies its heating eiTect in accordance with the voltage impressed thereon, an induction voltage regulator in control of the voltage impressed upon said heating means, said induction voltage regulator including an element which varies the voltageimpressed upon the heating means when moved, electric motor means to position said movable element, switching means in control of the energization of said motor means, a balancing potentiometer mechanically connected to said movable element, a control potentiometer, electromagnetic means to operate said switching means, and electrical connections between said electromagnetic means and potentiometers by which the energization of said electromagnetic means is controlled by the positions of said potentiometers.

3. In an electrically controlled heating system, in combination, electrical heating means which varies its heating effect in accordance with the voltage impressed thereon, an induction voltage regulator in control of the voltage impressed upon said heating means, said induction voltage regulator including an element which varies the voltage impressed upon the heating means when moved, three-phase reversible electric motor means to position said movable element, first and second relays, two energizing circuits for said motor means arranged to be completed by each of said relays, one set of said circuits operating said motor means in one direction and the other set operating the motor means in the other direction, double circuit switching means in control of the energization of said relays to selectively energize the same or deenergize both of them, a balancing potentiometer positioned by said movable element, a control potentiometer, electromagnetic means to operate said switching means and electrical connections between said potentiometers and electromagnetic means by which the energization of said electromagnetic means is varied upon movement of either of said potentiometers.

4. In an electrically controlled temperature control system, in combination, electrical temperature changing means of the type which varies its temperature changing effect upon variation of the voltage impressed thereon, a voltage regulator including a movable element operative to change the voltage impressed upon said temperature changing means upon movement of said-movable element, a source ofpower, a pair of electromagnetic coils connected in series across said source of power, a temperature responsive control potentiometer and a balancing potentiometer each having its resistance connected in parallel with the series-connected electromagnetic coils, connections between the junction of said electromagnetic coils and the contact elements of said potentiometers, resistance means associated with said potentiometers and electromagnetic coils operative to prevent complete short-circuiting of either electromagnetic coil upon movement of any potentiometer to an extreme position, a mechanical connection between said movable element and said balancing potentiometer, motor means in control of said movable element, and switching means controlled by the conjoint action of said electromagnetic coils in control of said motor means.

5. In an electrically controlled temperature control system, in combination, electrical temperature changing means of the type which varies its temperature changing efiect upon variation of the voltage impressed thereon, a voltage regulator including a movable element operative to change the voltage impressed upon said temperature changing means upon movement of said movable element, a source of power, a pair of electromagnetic coils connected in series across said source of power, a temperature responsive control potentiometer and a balancing potentiometer each having its resistance connected in parallel with the series connected electromagnetic coils, connections between the junction of said electromagnetic coils and the contact elements of said potentiometers, resistance means associated with said potentiometers and electromagnetic coils operative to prevent complete short-circuiting of either electromagnetic coil upon movement of any potentiometer to an extreme position, a mechanical connection between said movable element and said balancing potentiometer, motor means in control of said movable element, relay means including a pair of relay coils connected in series across a source of power in control of said motor means, and switching means controlled by the cooperative action of said electromagnetic coils operative to shunt one or the other of said relay coils whereby to render the other relay coil operative to control said motor means.

6. In an electrically controlled temperature control system, in combination, electrical temperature changing means of the type which varies its temperature changing effect upon variation of the voltage impressed thereon, a voltage regulator including a movable element operative to change the voltage impressed upon said temperature changing means upon movement of said movable element, a source of power, a pair of electromagnetic coils connected in series across said source of power, a temperature responsive control potentiometer and a balancing potentiometer each having its resistance connected in parallel with the series connected electromagnetic coils, connections between the junction of said electromagnetic coils and the contact elements of said potentiometers, resistance means associated with said potentiometers and electromagnetic coils operative to prevent complete short-circuiting of either electromagnetic coil upon movement of any potentiometer to an extreme position, a mechanical connection between said movable element and said balancing potentiometer, three phase motor means in control of said movable element, a pair of relays, two circuits controlled by each relay and connected to said motor means, one set. of circuits being operable to move said motor means in one direction aoeaaae and the other' set of circuits being operable to move said motor means in the other direction, and switching means in control of said relays controlled by the conjoint action of said electromagnetic coils.

'7. In an electrically controlled temperature control system, in combination, electrical temperature changing means of the type which varies its temperature changing effect upon variation of the voltage impressed thereon, a voltage regulator including a movable element operative to change the voltage impressed upon said temperature changing means upon movement of said movable element, a source of power, a pair of electromagnetic coils connected in series across said source of power, a temperature responsive control potentiometer and .a balancing potentiometer each having its resistance connected in parallel with the series-connected electromagnetic coils, connections between the junction of said electromagnetic coils and the contact elements of said potentiometers, resistance means associated with said potentiometers and electromagnetic coils operative to prevent complete short-circuiting of either electromagnetic coil upon movement of any potentiometer to an extreme position, three-phase motor means in controlof said movable element and balancing potentiometer, a pair of relays, two circuits controlled by each relay and connected to said motor means, one set of circuits being operable to move said motor means in one direction and the other set of circuits being operable to move said motor means in the other direction, balanced relay means in control of said relays comprising a pair of relay coils connected in series across said source of power, and double circuit switching means operative to selectively shunt one or the other of said relay coils controlled by the conjoint action of said electromagnetic coils.

LEWIS L. CUNNINGHAM. 

